Field of Invention
The invention relates to an optical touch system, a method of touch detection, a method of calibration and a computer program product.
Description of Related Art
In recent years, due to the convenience and intuitiveness on controlling, touch electronic products are favored by consumers and have become the mainstream in the market. In the resistive touch screen, the capacitive touch screen and the rear projection touch screen that are conventionally used in the electronic products, the capacitive touch screen has the best touch-sensing performance, but the manufacturing cost of the capacitive touch screen is the highest as well. Further, with the increase of the size of the touch screen, the manufacturing cost is also increased, so the application of the capacitive touch screen is limited.
To find an alternative for the capacitive touch screen, an optical touch screen employing an optical lens for detecting touch positions has been proposed due to various advantages including low cost and high accuracy. Since the optical touch screen is more advantageous in a competitive market, it is also a choice for the large size touch panel.
Another type of the optical touch screen employs a plurality of optical lenses or reflective frames disposed at edges of the screen for capturing images of user's fingers during the touch operation on the screen. The position of the shadow caused by the light shading effect of the finger in the captured image can be analyzed for calculating the precise position of the touch point. In addition, the cost of configuring the reflective frames is much lower than the cost of configuring the plurality of optical lenses, so using the reflective frames is advantageous on lowering the cost. Generally speaking, to cover the whole display panel in the illuminating range of the light emitting unit, the illumination intensity of the light emitting unit is required to maintain in a sufficient intensity. However, under such condition, when a touch object, such as a user's finger, is close to the light source, an image sensor may receive the reflected light reflected by the touch object in high intensity. Therefore, the light detector is overexposed to the reflected light, and a disablement or an error on detection occurs. On the other hand, if the light intensity of the light emitting unit is reduced to avoid detecting the high intensity reflected light, then the touch object on the region of the display panel which is away from the light emitting unit can be hardly detected. As a result, how to precisely detect the position of the touch object is still one of the problems for developing the optical touch system.